1. Field of the Invention
The present invention relates to control of movement of a wafer stage in one-shot exposure type exposure apparatus (including step-and-repeat type steppers), control of movement of the wafer stage and a reticle stage in exposure apparatus for performing the exposure operation in the reticle scanning method (including step-and-scan type steppers), and control of movement of the wafer stage and a sensor stage in wafer inspecting apparatus for performing inspection in the sensor scanning method and, more particularly, to a method of minimizing the overall turnaround time of stage movement for sequential exposure processes or sequential inspection processes in these apparatus.
2. Related Background Art
For carrying out processes such as exposures or inspections in a wafer provided with plural chip areas, higher production efficiency or inspection efficiency thereof is preferred. Particularly, focusing attention on movement of the stage upon change of chip areas being objects in the predetermined process such as exposure or inspection, the overall turnaround time necessary for the movement of stage through the all chip areas on the wafer needs to be shortened as much as possible. For that, the order of exposures or inspections or the like in the n(n>1) chip areas (i.e., a visit order of the chip areas) needs to be optimized so as to minimize the overall turnaround time necessary for the movement of stage.
For example, supposing that in a one-shot exposure type stepper there are n chip areas to be exposed on the wafer, a conceivable number of movements of the stage between the chip areas is at most nP2=n(n−1) (even under the condition that the turnaround time differs depending upon whether the direction of movement of the stage is positive or negative). Accordingly, once the exposure order or the inspection order of the all chip areas is determined, the overall turnaround time necessary for the movement of stage can be obtained uniquely and in short time. However, since there exists n! ways as to the orders for carrying out the exposures, inspections, or the like of the n chip areas, inordinate time is required for producing and checking all conceivable orders and for computing all applicable solutions. Particularly, when n>13, it is practically impossible (“Practical course: Invitation to traveling-salesman problems I, II, III,” Operations Research 39 (1994), No. 1: pp 25-31, No. 2: pp 91-96, No. 3: pp 156-162).
Further, in the case of the apparatus for carrying out scanning exposure or scanning inspection, typified by the scan exposure type steppers, the reticle stage (or a sensor stage) and the wafer stage need to be controlled in synchronism upon carrying out the exposure, inspection, or the like for each shot area (equivalent to the chip area) on the wafer, and there are degrees of freedom as to scan directions in each shot area. Therefore, the exposure order (exposure sequence) for the all shot areas and the scan directions of local areas (for example, areas successively becoming exposure objects) in the respective shot areas must be optimized simultaneously. The number of conceivable exposure sequences or inspection sequences (either of which is included in the movement sequence) is given by the product of the number of combinations with the scan directions of local areas in the respective n shot areas (if the degrees of freedom of the scan directions are m, the number of combinations is mn) and the number of permutation of exposures (or inspections) of the n shot areas (n!), i.e., mn×n!. It is thus more difficult to obtain an optimum solution of movement sequence than in the case of the one-shot exposure type steppers.
In the conventional apparatus described above, therefore, optimum simultaneous control sequences of the wafer stage and reticle stage to minimize the turnaround time of exposure sequence under specific conditions anticipated are preliminarily set in order to shorten the time for successive exposures of plural areas on the wafer within practical computation time. When an actual operation condition does not suit the above specific conditions, only an unfit portion of the optimum simultaneous control sequences preset is modified so as to fit the above specific conditions. Accordingly, recomputation of optimum movement sequences is not carried out each time in the practical operations.